OKLAHOMA CITY -- Eric Kennedy Phan has pleaded guilty on Thursday to two counts of first-degree murder in the death of Lauren Barnes and her unborn child, prosecutors said.

VIDEO: Family Reacts To Eric Phan's Guilty Plea | Eric Phan Pleads Guilty To Murders

Sentencing is scheduled for Oct. 17. The 21-year-old faces either life in prison or life in prison without parole.

The Oklahoma state medical examiner said Barnes, 20, was asphyxiated, and Phan told a friend that he choked her to death. Barnes was found dead in Nov. 2007 at the Stinchcomb Wildlife Refuge after a weeklong search.

According to an affidavit released last year by Oklahoma County District Court officials, Phan's best friend -- David Huynh -- told investigators that Phan told him that he choked Barnes and that "the last thing she said to him was that she would get an abortion."

Huynh told authorities that Phan told him that he thought he broke her neck. The affidavit stated that Phan started crying and told Huynh that he dumped Barnes at Stinchcomb.

Her friends called Barnes happy and fun-loving, but they said that more than anything else, she was looking forward to becoming a mother. Barnes was five months pregnant.

"She was excited. She was ready. She would have been a great mother," said Vanessa Ghiassi.

"She was happy to be pregnant -- very happy. Every time she talked about it, she'd glow -- every time," said Fashion Burch. "If she was still around, she'd be like, 'Wow, people care about me that much.'"

"Lauren was the light of everyone else's party. She was always funny, always laughing," said Sheli Lemieux, Barnes' aunt.